fix: make only a single SELECT to get inserted default and generated values of multiple entities

src/query-builder/ReturningResultsEntityUpdator.ts

@@ -117,26 +117,29 @@ export class ReturningResultsEntityUpdator {
         // for postgres and mssql we use returning/output statement to get values of inserted default and generated values
         // for other drivers we have to re-select this data from the database
         if (this.queryRunner.connection.driver.isReturningSqlSupported() === false && insertionColumns.length > 0) {
-            await Promise.all(entities.map(async (entity, entityIndex) => {
+            const entityIds = entities.map((entity) => {
                 const entityId = metadata.getEntityIdMap(entity)!;
-
-                // to select just inserted entity we need a criteria to select by.
-                // for newly inserted entities in drivers which do not support returning statement
-                // row identifier can only be an increment column
-                // (since its the only thing that can be generated by those databases)
-                // or (and) other primary key which is defined by a user and inserted value has it
-
-                const returningResult: any = await this.queryRunner.manager
-                    .createQueryBuilder()
-                    .select(metadata.primaryColumns.map(column => metadata.targetName + "." + column.propertyPath))
-                    .addSelect(insertionColumns.map(column => metadata.targetName + "." + column.propertyPath))
-                    .from(metadata.target, metadata.targetName)
-                    .where(entityId)
-                    .setOption("create-pojo") // use POJO because created object can contain default values, e.g. property = null and those properties maight be overridden by merge process
-                    .getOne();
-
-                this.queryRunner.manager.merge(metadata.target as any, generatedMaps[entityIndex], returningResult);
-            }));
+                return entityId;
+            });
+
+            // to select just inserted entities we need a criteria to select by.
+            // for newly inserted entities in drivers which do not support returning statement
+            // row identifier can only be an increment column
+            // (since its the only thing that can be generated by those databases)
+            // or (and) other primary key which is defined by a user and inserted value has it
+
+            const returningResult: any = await this.queryRunner.manager
+                .createQueryBuilder()
+                .select(metadata.primaryColumns.map(column => metadata.targetName + "." + column.propertyPath))
+                .addSelect(insertionColumns.map(column => metadata.targetName + "." + column.propertyPath))
+                .from(metadata.target, metadata.targetName)
+                .where(entityIds)
+                .setOption("create-pojo") // use POJO because created object can contain default values, e.g. property = null and those properties maight be overridden by merge process
+                .getMany();
+
+            entities.forEach((entity, entityIndex) => {
+                this.queryRunner.manager.merge(metadata.target as any, generatedMaps[entityIndex], returningResult[entityIndex]);
+            });
         }
 
         entities.forEach((entity, entityIndex) => {

test/github-issues/6266/entity/Post.ts

@@ -0,0 +1,14 @@
+import { PrimaryGeneratedColumn, Entity, Column, CreateDateColumn } from "../../../../src";
+
+@Entity()
+export class Post {
+
+    @PrimaryGeneratedColumn()
+    id?: number;
+
+    @Column()
+    title: string;
+
+    @CreateDateColumn()
+    readonly createdAt?: Date;
+}

test/github-issues/6266/issue-6266.ts

@@ -0,0 +1,60 @@
+import "reflect-metadata";
+import {
+    closeTestingConnections,
+    createTestingConnections,
+    reloadTestingDatabases,
+} from "../../utils/test-utils";
+import { Connection } from "../../../src/connection/Connection";
+import { Post } from "./entity/Post";
+import sinon from "sinon";
+import { SelectQueryBuilder } from "../../../src";
+import { assert } from "chai";
+
+describe("github issues > #6266 Many identical selects after insert bunch of items", () => {
+    let connections: Connection[];
+    const posts: Post[] = [
+        {
+            title: "Post 1",
+        },
+        {
+            title: "Post 2",
+        },
+        {
+            title: "Post 3",
+        },
+        {
+            title: "Post 4",
+        },
+    ];
+
+    before(
+        async () =>
+            (connections = await createTestingConnections({
+                entities: [__dirname + "/entity/*{.js,.ts}"],
+                enabledDrivers: ["mysql"],
+            }))
+    );
+    beforeEach(() => reloadTestingDatabases(connections));
+    after(() => closeTestingConnections(connections));
+
+    it("should execute a single SELECT to get inserted default and generated values of multiple entities", () =>
+        Promise.all(
+            connections.map(async (connection) => {
+                const selectSpy = sinon.spy(
+                    SelectQueryBuilder.prototype,
+                    "select"
+                );
+
+                await connection
+                    .createQueryBuilder()
+                    .insert()
+                    .into(Post)
+                    .values(posts)
+                    .execute();
+
+                assert.strictEqual(selectSpy.calledOnce, true);
+
+                selectSpy.restore();
+            })
+        ));
+});